The present application relates to devices for dispensing a predetermined volume of liquid, as for example, for medication, and in particular to an adjustable device in which the user can select one of a plurality of volumes of liquid to be dispensed.
Certain liquids, for example liquid medication, are needed in small predetermined amounts, and therefore it is desirable to have a dispensing device for dispensing predetermined amounts of liquid. In my U.S. Pat. No. 4,892,232 I disclosed such a device.
The amount of medication needed by a first patient may be different from the amount of medication needed for a second patient, and therefore it is also desirable to provide an adjustable dispensing device whereby the operator can operate a selector device and choose the desired volume of liquid that the dispenser will dispense. An adjustable dose dispenser having a plurality of different sized metering chambers with a stem rotatable to select the chamber to be discharged was disclosed in my U.S. Pat. No. 5,085,351. In this device, each of the metering chambers has a flexible wall.
As an alternative to selecting one of a plurality of chambers for varying the volume of fluid to be dispensed, a device can be configured with a single chamber where the volume dispense from the chamber is adjustable. This can be accomplished by providing a piston for dispensing the liquid from the chamber where the length of the piston stroke is adjustable, as disclosed in my previously issued U.S. Pat. No. 5,813,187.
One disadvantage of the adjustable dose dispenser as disclosed in my U.S. Pat. No. 5,085,351 is that the flexible member which forms the metering chambers thereof may yield over time, causing the volume dispensed to change. The piston operated dispensing device of my U.S. Pat. No. 5,183,187, on the other hand, has rigid walls such that the volume of liquid dispensed for any given setting thereof should remain constant through the life of the apparatus.
One problem with the piston operated device of my U.S. Pat. No. 5,183,187 is that the volume of liquid being dispensed is adjusted by rotating the stem of the dispensing valve and the valve stem is connected to the piston and a threaded member. To operate properly, however, the piston is sealed against the cylindrical wall of the metering chamber and the seal around the perimeter of the piston creates resistance, inhibiting the manual rotation of the dispensing stem.
Another problem with the existing piston operated dispenser is that the device includes a spring for urging the piston in a direction that maximizes the volume of the metering chamber and the other end of the spring is fitted against a surface of the housing of the valve such that on rotation of the stem either the piston rotates with respect to the spring or the spring rotates with respect to the housing. In either case the movement of the plastic of the housing or of the piston against the spring causes particles of plastic to enter the liquid being dispensed. The continuing use of the dispenser causes those particles to obstruct the small passages that extend through the stem of the dispenser and thereby inhibit its operation.
There is therefore, a need for an improved piston operated dispensing apparatus in which the volume of liquid being dispensed may be more easily adjusted and which will not cause small particles of plastic to be released into the liquid.
Briefly, the present invention is embodied in a dispensing apparatus for dispensing one of a plurality of predetermined volumes of a liquid. The device includes a container for retaining pressurized liquid and a valve assembly that extends into the container. The valve assembly includes an elongated stem having a first end extending outward of the container and a second end extending inward of the container, the valve assembly also having a longitudinal axis. The valve assembly also includes a valve housing having an inner wall that defines a metering chamber. At the bottom end of the metering chamber is a longitudinally movable piston having a first surface that defines a wall of the metering chamber and a second surface that is in contact with the pressurized liquid.
The elongated stem is axially movable with respect to the valve housing between a first position in which the metering chamber is in communication with the reservoir and a second position in which the metering chamber is in communication with the ambient. The piston is axially moveable with respect to the stem between a first stop which defines a maximum volume of the metering chamber and a second stop which defines the minimum volume of the metering chamber. The stem is axially rotatable with respect to the piston such that rotation of the stem will not cause rotation of the piston. A sliding float member is fitted around the stem within the chamber and is axially slidable with respect to the stem but is locked for rotation with the stem, and the lower surface thereof abuts, and floats above the first surface of the piston.
In accordance with one feature of the invention, a prong is provided in the stem and a spring extends between the prong on the stem and the sliding float for urging the stem axially outward of the container and for urging the piston in a direction which maximizes the volume of the metering chamber. Since both the sliding float member and the prong rotate with the stem, rotation of the stem will not cause movement of a plastic surface against the metal of the spring. Accordingly, the rotation of the stem will not cause friction between a plastic surface and the spring causing particles of plastic to enter into the liquid being dispensed.
In accordance with another feature of the invention, the valve housing has a plurality of contact surfaces with each of the contact surfaces being of different angular orientations about the axis thereof and at different longitudinal positions with respect to the axis. The slide also has a contact surface which is rotatable with the stem such that the contact surface of the slide is rotatable into alignment with any one of the plurality of contact surfaces on the valve housing for selecting one of a plurality of predetermined volumes of liquid to be dispensed.